Six morphological forms pertaining to the concept of Brown Brocket adopted here have been described as subspecies of Mazama simplicicornis (= M. gouazoubira) or M. gouazoubira ( Pinder and Leeuwenberg 1997). They are argentina Lönnberg, auritus Gray, kozeritzi Miranda-Ribeiro, mexianae Hagmann, namby Fitzinger, and superciliaris Gray. In his review of Brazilian species of Mazama, Rossi (2000) interpreted the morphological differences that led authors to describe auritus Gray, kozeritzi Miranda-Ribeiro, mexianae Hagmann, namby Fitzinger, and superciliaris Gray as individual variation among specimens of Mazama gouazoubira. We follow this author in not recognizing any subspecies from Brazil. The form argentina Lönnberg , not analyzed by Rossi (2000), remains the only one that could merit subspecific status. Nevertheless, a thorough analysis of the original description of Mazama simplicicornis argentina shows there are no characters in the type that cannot be explained by individual or geographical variation. Therefore, at the present time we see no reason to recognize either argentina Lönnberg or any other form cited above as subspecies of Mazama gouazoubira.

Justification:
This species is considered to be Least Concern in view of its relatively large distribution, occurrence in a number of protected areas, presumed large populations which do not appear to be declining at a rate sufficient for a threat category at this time. Recent studies indicate that the distribution and abundance of the species do not warrant a threatened status at this time although populations are declining where they come in contact with human populations.

The brown brocket deer is found east of the dry, pre-Andean regions in Argentina and Bolivia, extending to the Atlantic coast on the west; its northern limit is south of the Amazon region and its southern limit includes all of Uruguay and up to the province of Entre Rios in Argentina. Although some authors report its distribution throughout all of Brazil, more recent evidence indicates its substitution by M. nemorivaga in the region of the Amazon (Duarte 1996; Duarte and Jorge 1998; Rossi 2000; Weber and Gonzalez 2003).

Populations seem to be decreasing due to the advance of human populations. There is no evidence of fragmented populations and the species continues to be abundant in most of its range, decreasing or disappearing when close to human populations. Densities vary greatly. In Brazil densities of 0.35 – 1 individual/km² have been found (Pinder 1997); in Bolivia densities of 5-12 individuals/km² have been found (Rivero et al. 2004).

This species occurs in moderately humid to dry regions where there are areas of woody or brush cover. It is not found in the Amazon region and it avoids dense forests in other regions as well, although it occupies the edges of forests. It does not live in open areas but will feed in these areas, including many types of agricultural plantations, if cover is available nearby. It is found in both dry and moist Chaco regions (Cartes 1998; Chiarello 1999; Gonzalez 2004; Pinder 1997; Pinder and Leeuwenberg 1997; Rivero et al. 2005).

It eats a wide variety of plant species and is a selective feeder. It has pulses of frugivory depending on the area, season and availability of frutis, but is not essentially frugiverous in many areas; its habitat is not consistent with a frugivorous diet since it avoids forests where most of the fruit is found (Caballero 2001; Cartes 1998; Julia 2002; Pinder 1997; Stallings 1984).

Breeding occurs almost all year around with births in all months except May, June and July in Argentina and Bolivia and correlated with the rainy season in Brazil (Chavez 1999; Julia 2002). There is a post partum estrus and a gestation period of 7 months.

Mazama gouazoubira is a small to medium sized deer, with head and body length 882-1060 mm, tail length 83-190 mm, and ear length 95-121 mm (Rossi, 2000); shoulder height 500-650 mm and weight 11-25 kg (Duarte and Jorge 1998). In Brazil, regional, ecological and individual variations in coloration of M. gouazoubira have frequently been reported (Duarte 1996; Pinder and Leeuwenberg 1997; Rossi 2000). Light and brownish colors prevail in individuals living in grasslands, while forest populations tend to be darker and grayer; significant individual variation exists within a single population. M. gouazoubira can be readily distinguished from the most similar species, the Amazonian brown brocket Mazama nemorivaga, by its orange rump and dorsal side of the tail, larger rounded ears, smaller eyes and orbital cavities, and wider auditory bulla rather than chocolate brown rump and dorsal side of the tail, small pointed ears, large eyes, large orbital cavities, and narrow auditory bulla of the latter species (Duarte 1996; Rossi 2000).

In Argentina populations are generally declining due to hunting pressure and habitat loss. International hunting expeditions are organized in Argentina (Julia 2002). In Bolivia the populations seem to be staying constant in spite of great hunting pressure. In Brazil this is the most abundant deer species in the country, but populations are declining in certain areas (Rio Grande do Sul, Rio de Janeiro). In Paraguay, the populations in general are remaining constant, but the species has disappeared from recently urbanized areas and areas of high human density. In general there is heaving hunting pressure and loss of animals due to kills by dogs as well as habitat loss.

The species occurs in a number of protected areas throughout its distribution: 5 national parks and 9 provincial reserves in Argentina; in almost all national parks and private reserves in Paraguay; in 7 national protected areas in Bolivia and in numerous protected areas in Brazil. Hunting is illegal in many places (several Argentine provinces, for example) but the bans are not enforced. Recommended actions would be to implement and enforce controls on hunting, control stray dogs and to educate rural and village populations to conserve the deer rather than immediately trying to kill any individual that they see in the area.